Electrical cartridge type heaters are a versatile kind of electrical heaters, in which an electrical heating element, which is typically configured as a hot wire or resistance wire, is arranged in the interior space of an outer jacket, the jacket often, but not necessarily, being formed by a tube, especially by a tube with a circular cross section. In this connection, this kind comprises, in addition to cartridge type heaters with only one metallic jacket, also hollow cartridges, which have a second, inner, often likewise tubular metallic jacket.
It is important in many applications in which such electrical cartridge type heaters are employed to monitor the operation of the electrical cartridge type heater, and it often is a question of reaching or maintaining a temperature at one or more points of the electrical cartridge type heater within a predefined temperature window as well. In order to make this possible, it is known, e.g., from DE 20 2008 014 050 U1 and DE 20 2007 010 865 U1 to arrange a temperature sensor or a temperature probe or an integrated thermocouple in the interior of the electrical cartridge type heater, which is, however, usually sensitive to pressure, which is to be taken into consideration in case of a crimping or compressing of the cartridge type heater. In addition, only a local monitoring of the temperature at one point is achieved in this way, so that a temperature deviation occurring at another point can only be detected if it has an effect on the locally monitored point.
Electrical heating elements with a temperature-dependent resistance behavior are known from DE 203 21 257 U1, for example.